How To Fix A Central Heating Thermostat


When all your radiators go cold — or get hot when you don’t want them to — the first thing to check is your room thermostat.

1. Make sure it is on the right setting — 15°C in a hallway. 21°C in a living room. If you turn the dial back and forth, you should hear a click as the thermostat operates: no click means that it is faulty and should be checked or replaced.

how to fix a central heating thermostatCheck, too, that the thermostat isn’t giving a faulty reading be cause of some outside source: a strong draught. A fire nearby or sunlight can all affect it.

2. If all is well. Move to the programmer/timeswitch. Start by checking that it shows the correct time: a momentary power cut could have zeroed it while you were out.

Next make sure that the programme settings are correct —they’re easy to get wrong or knock out of adjustment.

If the programmer seems ‘dead’. Turn off the power supply and unscrew it from its backing box. Check that the power ‘in’ connections are sound and that plugin connections between the unit and backing box haven’t become dirty or loose.

If turning the programmer to ‘constant’ has no effect on the boiler or pump, check the connections to these two components — again making sure the power is switched ‘off’. Loose terminals or frayed flexes should be easy to spot: if necessary, replace the defective wires using heatproof flex.

If your system includes thermostatic control valves on the hot water primary circuit supplying the cylinder, or motorized valves to distribute boilerheated water between the hot water circuit and the radiator circuit, you may experience trouble due to jamming or failure of the motors.

Electrical connections and cable runs are basically simple; keep wiring and maker’s instructions handy to deal with problems quickly.

The most common symptom, assuming the programmer is working, is that either the hot water or the heating valves don’t work when they should.

You’ll find such valves near the boiler or the cylinder. With the system switched to ‘constant’, feel by hand that hot water is being distributed through them.

3. On a motorized valve, check that the connections to the motor haven’t become loose.

4. On some systems, thermostatic valves are fitted to individual radiators to give localized heating control. These are mechanical in operation, and sometimes they jam.

Depending on the make of valve, you may be able to dismantle it and free the temperaturesensing bellows controlling the flow, but drain the system before doing so.

5. It may be stating the obvious, but check the boiler thermostat as well. Instructions on the boiler unit will tell you the correct setting, while you can check it’s working by turning the dial and listening for a click. Check the sender ‘capillary between the thermostat and heat exchanger it mustn’t be kinked or dislodged.

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